1. Field of the Invention
The present invention relates to a toner for developing an electrostatic charge image which is useful for electrography, particularly for a printer or the like employing a developing method of a one component system. More particularly, the present invention relates to a toner for developing an electrostatic image, which has a low softening point required for a low temperature fixing property and which is substantially free from fusion to a developing blade or other components of a developing apparatus even when it is applied to a developing system where durability is required and substantially free from a change in image quality caused by such fusion.
2. Discussion of Background
Dry developing systems to be used for electrography generally include a two component developing system employing a carrier and a toner as mixed, and a one component developing system employing no carrier. Among them, the two component developing system employs a carrier such as iron powder, ferrite powder, or the like, whereby a so-called toner concentration control mechanism is required to supplement a necessary amount of the toner as the toner is consumed. Therefore, the two component developing system has had problems with respect to the large size of the apparatus and the high cost. On the other hand, the one component developing system includes a magnetic one component system and a non-magnetic one component system, and an apparatus for either system can be made to be small-sized. Accordingly, in recent years, this system has been employed in many cases including personal type and full color type copying machines and printers which have been increasingly popular.
In recent years, copying machines, printers, etc. are required to have a high performance. The performance which a toner is required to have, may, for example, be such that when an image is formed, the image density is sufficient, and the image has no defect, that it can be used constantly for a long period of time, that it will sufficiently fix to paper, and that it is free from blocking during the process for its production or during its storage for transportation, and thus covers various requirements from the process for production of the toner to the image forming. Among such requirements, there are some which tend to be opposing to each other and tend to be hardly satisfied simultaneously, like the requirement that it can be used constantly for a long period of time and that it will sufficiently fix to paper. To cope with such requirements, many proposals have been made with respect to the natures of the respective components constituting the toner, the blend formulation, the production method, the production conditions, etc.
However, depending upon various phenomena and transfer systems employed for image-forming devices, there have been cases where conventional toners can provide no adequate effects to the required performances. Especially when it is attempted to lower the energy (the temperature) of the fixing device in order to reduce the power consumption or to accomplish high speed printing, if the toner fails to melt sufficiently at the low temperature, the fixing failure will result. Accordingly, it has been common to lower the softening point or the glass transition point of the binder resin. However, in a one component developing system wherein a substantial load is exerted to a toner, such a method brings about fusion to a blade for regulating the toner layer on a developing roll during a continuous copying operation or to a toner transport roller or a fixing roller and thus has been a cause for e.g. deterioration in the uniformity in the image quality or formation of stria. Further, in the production of the toner containing a binder resin with a low softening point or glass transition point, its fusion to the production apparatus, or the like, is likely to take place, whereby there has been a problem such as a decrease in the yield of the toner as a product, or necessity of a step of cleaning the apparatus.
Such problems have been distinct particularly in copying machines or printers for high speed printing or large size printing. For example, it has been difficult to obtain a toner which can be used for an image-forming device of a low temperature heat fixing system employing a heat roll with a surface temperature of at most 150° C. and which sufficiently satisfies a performance not to fuse to a blade or a toner transport roller, and it has been unknown how to obtain such a toner.